larsoner · larsoner · Mar 15, 2016 · Mar 14, 2016 · Mar 14, 2016
diff --git a/.travis.yml b/.travis.yml
@@ -39,7 +39,7 @@ install:
         if [ "$PYTHON_VERSION" == "2.7" ]; then
           conda install --yes --quiet mayavi;
           conda upgrade --yes --all;
-          conda upgrade --yes pyface;
+          pip install --upgrade pyface;
         fi;
       fi;
     - pip install -r requirements.txt

diff --git a/examples/plot_quantum.py b/examples/plot_quantum.py
@@ -0,0 +1,52 @@
+# -*- coding: utf-8 -*-
+r"""
+======================
+Some Quantum Mechanics
+======================
+
+We start with a two spin system :math:`\uparrow` and :math:`\downarrow`
+
+"""
+# Author: Óscar Nájera
+
+from __future__ import division, absolute_import, print_function
+
+
+def hamiltonian(M, mu):
+    r"""Generate a single orbital isolated atom Hamiltonian in particle-hole
+    symmetry. Include chemical potential for grand Canonical calculations
+
+    .. math::
+        \mathcal{H} - \mu N = M(n_\uparrow - n_\downarrow)
+        - \mu(n_\uparrow + n_\downarrow)
+    """
+    pass
+
+###############################################################################
+# Double occupation
+# -----------------
+#
+# To find out the double occupation one uses the relation
+# (Works in Sphinx-Gallery)
+
+import matplotlib.pylab as plt
+import numpy as np
+x = np.linspace(0, 1, 20)
+plt.plot(x, (1 - x**2) / 4)
+plt.ylabel('$\\langle n_\\uparrow n_\\downarrow \\rangle$')
+plt.show()
+
+###############################################################################
+#
+# .. math:: \langle n_\uparrow n_\downarrow \rangle = \frac{2\langle V \rangle}{U}+\frac{1}{4}
+
+print('pass')
+
+###############################################################################
+# (Does not work in Sphinx-Gallery)
+# ---------------------------------
+
+plt.plot(x, (1 - x) / 4)
+plt.ylabel(r'$\langle n_\uparrow n_\downarrow \rangle$')
+plt.xlabel('U')
+plt.show()